1. Field of the Invention
This invention relates to optically coupled remote control systems, and more particularly to optically coupled systems for controlling the operation of marine loading arms.
2. Description of the Prior Art
Fluid loading arms constructed of articulated pipe are extensively used in the petroleum industry for transferring oil or other fluids between a jetty, wharf, or other loading station and a marine tanker moored alongside. Such an arm generally comprises an inboard boom or limb supported on a vertical riser pipe by pipe swivel joints to facilitate pivotal movement about horizontal and vertical axes, and an outboard boom or limb connected by a pipe swivel joint to the inboard limb so as to be pivotal relative thereto about a horizontal axis. The outer end of the outboard limb is adapted to be connected to a pipe manifold on a tanker located within the reach of the arm, such as by a remotely controlled coupler device.
Various electrically controlled actuators are used to open and close hydraulic valves which control fluid under pressure to raise and lower the outboard end of each of the limbs of the articulated arm, rotate the articulated arm about the riser pipe, connect and disconnect the outboard end of the arm from the tanker manifold and control the flow of fluid through the loading arm. Due to the possible presence of explosive vapors in the area surrounding the articulated loading arm, the design of the prior art electrical circuits is strictly regulated. Such regulation causes the design and construction of the prior art articulated loading arm to be rather expensive. The various switches, relays and other possible sources of electrical sparks must each be enclosed in an air-tight container. The explosion-proof containers about the various portions of the prior art equipment also cause the apparatus to be somewhat bulky. It is therefore important that a cheaper and more compact system be provided for controlling the operation of articulated loading arms in a potentially explosive environment.